The invention relates to a piston engine or machine which has at least one dry-running piston-cylinder unit.
Such piston engines are known and are referred to, for example, as so-called crosshead-piston engines or machines. Such machines employ a two-part piston. A first, upper piston section together with the walls of the cylinder define the cylinder volume. A second, lower piston section extends into the lower portion of the cylinder and is spaced apart from the first piston section by a piston bar. This lower portion of the cylinder forms means for lubricating the second piston area. The lower and upper portions of the cylinder are sealed with respect to each other, and the piston bar between the two cylinder sections extends through the seal. In this manner, the upper section of the piston in such a known crosshead-piston engine runs without additional lubricant in the cylinder. The advantage of such a dry-running cylinder is that no lubricant enters the compression space of the cylinder. As a result, when the piston-cylinder unit is used as a compressor, no lubricant becomes entrained in the gas as it is being compressed. When the piston-cylinder unit is used as a pump, no lubricant enters in the fluid that is being pumped. Even when the dry-running piston engine is used as a combustion engine, no lubricant enters the combustion space, which improves the quality of the exhaust gases.
Such a crosshead-piston engine is relatively voluminous and complex due to the two-part piston and the associated, relatively long cylinder required thereby.